1. Field of the Invention
Embodiments disclosed herein relate to catalysts useful for the alkylation of aromatic compounds. More particularly, embodiments relate to catalysts having lower deactivation rates during use. Still more particularly, embodiments relates to an extruded zeolite catalyst which has an inert, porous coating that maintains a liquid phase within the pores of the catalyst.
2. Background Art
The alkylation of aromatic compounds with olefins is an established commercial technology. For example, benzene alkylated with short chain hydrocarbons (typically having 2 to about 6 carbon atoms) has value as a gasoline octane enhancer. Light aromatic compounds alkylated with longer chain (that is, having greater than about 8 to 10 carbon atoms) linear olefins are commonly sulfonated to produce surfactants suitable for use in detergent manufacture.
The alkylation of benzene and other light aromatic compounds has typically been carried out using hydrofluoric acid or a solid acid catalyst in a fixed bed, plug flow process. For example, U.S. Pat. No. 2,860,173 discloses the use of a solid phosphoric acid as a catalyst for the alkylation of benzene with propylene to produce cumene. More recently, the use of Friedel Crafts catalysts, especially aluminum chloride and certain natural zeolites and synthetic commercial sieves, as alkylation catalysts has been taught.
Still more recently, alkylation of benzene and light aromatics with C6/C30 olefin co-fed with the aromatics over a solid catalyst bed in a reactive distillation column has been carried out in a reactive distillation column (U.S. Pat. No. 5,770,782).
Solid acid alkylation catalysts tend to deactivate rapidly in the presence of dialkylated aromatic products. Carbonaceous deposits and heavy organics build up on the catalyst surface, with a resultant decrease in catalyst effectiveness and a need to shut the process down to regenerate the catalyst. This tends to be related to the exothermic nature of the reaction, which has a tendency to be severe and difficult to control.
Regeneration is typically provided using benzene maintained in the liquid phase at a pressure of at least 500 psig and temperatures in excess of 250° C. Ethyl benzene and cumene have traditionally been produced by the reaction of benzene and the respective olefin, i.e., ethylene and propylene in the presence of an acidic catalyst. In some known processes, the catalyst is highly corrosive and has a relatively short life, e.g., AlCl3, H3PO4 on clay, BF3 on alumina, and others require periodic regeneration, e.g., molecular sieves. The exothermicity of the reaction and the tendency to produce polysubstituted benzene require low benzene conversions per pass with large volume recycle in conventional processes.
Recently a method of carrying out catalytic reactions has been developed, wherein the components of the reaction system are concurrently separable by distillation, using the catalyst structures as the distillation structures. Such systems have been applied to aromatic alkylation as in U.S. Pat. Nos. 4,950,834, 4,849,569; 5,019,669; 5,043,506; 5,055,627; 5,086,193; 5,176,883; 5,215,725; 5,243,115; and 5,321,181. A catalyst/distillation structure described is a cloth belt with a plurality of pockets spaced along the belt, which is then wound in a helix about a spacing material such as stainless steel knitted mesh. These units are then disposed in the distillation column reactor. These patents all specifically disclose the use of A, X, Y, L, erionite, omega, mordenite, and beta zeolites as the catalyst in the catalytic distillation structure. In addition, U.S. Pat. No. 4,443,559 discloses a variety of catalyst structures for this use and is incorporated herein.
Zeolites normally foul rapidly in the presence of olefin vapors during the alkylation of benzene. This shortens the catalyst life in service for producing alkyl aromatics, i.e., ethyl benzene (EB), cumene and butylbenzene. One solution to this has been to operate such that the catalyst is always immersed in a liquid phase as in U.S. Pat. No. 4,891,458. Catalyst stability is a major component of advancing benzene alkylation technology. The prior structures disclosed in U.S. Pat. Nos. 4,215,011; 4,232,177; 4,242,530; 4,250,052; 4,302,356; and 4,307,254 presumably provided a barrier between the catalyst and the vapor phase olefin. This mass transfer barrier also lowered the effective catalyst activity. Using the catalyst in wire mesh structure triples the catalyst mass activity. However, the catalyst rapidly deactivates: (k/ko˜exp[−0.003t(hr)]).
In one commercial process, a fixed bed reactor operates in liquid phase with olefin content below the liquid saturation level, which increases process costs. In another commercial process, a multi-phase reactor operates with the catalyst enclosed in liquid filled fiberglass bags, which introduces a liquid film through which the olefin must pass to get to the catalyst and mass transfer limitations slow the reaction rate.
What is still needed therefore, are methods and catalysts that can provide increased run times, while maintaining useful activity rates.